<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>window对象</title>
</head>
<body>
    <script type="text/javascript">
        var a = 3;
        console.log(window.a);
        function hello(){
            alert(window.a);
        }
        window.hello();
    </script>

</body>
</html>